Mojo: Armed Watchers

third_party/WebKit/Source/core/mojo/MojoWatcher.cpp

Index: third_party/WebKit/Source/core/mojo/MojoWatcher.cpp
diff --git a/third_party/WebKit/Source/core/mojo/MojoWatcher.cpp b/third_party/WebKit/Source/core/mojo/MojoWatcher.cpp
index 804536d40d710b92a73294c1b43e30129550f58e..2175d06ca7899b0c915eef13c811fea95380d79c 100644
--- a/third_party/WebKit/Source/core/mojo/MojoWatcher.cpp
+++ b/third_party/WebKit/Source/core/mojo/MojoWatcher.cpp
@@ -20,6 +20,7 @@ static void runWatchCallback(MojoWatchCallback* callback,
   callback->call(wrappable, result);
 }
 
+// static
 MojoWatcher* MojoWatcher::create(mojo::Handle handle,
                                  const MojoHandleSignals& signalsDict,
                                  MojoWatchCallback* callback,
@@ -27,8 +28,8 @@ MojoWatcher* MojoWatcher::create(mojo::Handle handle,
   MojoWatcher* watcher = new MojoWatcher(context, callback);
   MojoResult result = watcher->watch(handle, signalsDict);
   // TODO(alokp): Consider raising an exception.
-  // Current clients expect to recieve the initial error returned by MojoWatch
-  // via watch callback.
+  // Current clients expect to recieve the initial error returned by
+  // MojoRegisterWatcher via watch callback.
   //
   // Note that the usage of wrapPersistent is intentional so that the intial
   // error is guaranteed to be reported to the client in case where the given
@@ -39,45 +40,21 @@ MojoWatcher* MojoWatcher::create(mojo::Handle handle,
         BLINK_FROM_HERE, WTF::bind(&runWatchCallback, wrapPersistent(callback),
                                    wrapPersistent(watcher), result));
   }
+
   return watcher;
 }
 
-MojoWatcher::MojoWatcher(ExecutionContext* context, MojoWatchCallback* callback)
-    : ContextLifecycleObserver(context),
-      m_taskRunner(TaskRunnerHelper::get(TaskType::UnspecedTimer, context)),
-      m_callback(this, callback) {}
-
 MojoWatcher::~MojoWatcher() {
   DCHECK(!m_handle.is_valid());
 }
 
-MojoResult MojoWatcher::watch(mojo::Handle handle,
-                              const MojoHandleSignals& signalsDict) {
-  ::MojoHandleSignals signals = MOJO_HANDLE_SIGNAL_NONE;
-  if (signalsDict.readable())
-    signals |= MOJO_HANDLE_SIGNAL_READABLE;
-  if (signalsDict.writable())
-    signals |= MOJO_HANDLE_SIGNAL_WRITABLE;
-  if (signalsDict.peerClosed())
-    signals |= MOJO_HANDLE_SIGNAL_PEER_CLOSED;
-
-  MojoResult result =
-      MojoWatch(handle.value(), signals, &MojoWatcher::onHandleReady,
-                reinterpret_cast<uintptr_t>(this));
-  if (result == MOJO_RESULT_OK) {
-    m_handle = handle;
-  }
-  return result;
-}
-
 MojoResult MojoWatcher::cancel() {
-  if (!m_handle.is_valid())
-    return MOJO_RESULT_OK;
+  if (!m_watcherHandle.is_valid())
+    return MOJO_RESULT_INVALID_ARGUMENT;
 
-  MojoResult result =
-      MojoCancelWatch(m_handle.value(), reinterpret_cast<uintptr_t>(this));
+  m_watcherHandle.reset();
   m_handle = mojo::Handle();
-  return result;
+  return MOJO_RESULT_OK;
 }
 
 DEFINE_TRACE(MojoWatcher) {
@@ -90,25 +67,87 @@ DEFINE_TRACE_WRAPPERS(MojoWatcher) {
 }
 
 bool MojoWatcher::hasPendingActivity() const {
-  return m_handle.is_valid();
+  return !!m_context;
 }
 
 void MojoWatcher::contextDestroyed(ExecutionContext*) {
   cancel();
 }
 
+MojoWatcher::MojoWatcher(ExecutionContext* context, MojoWatchCallback* callback)
+    : ContextLifecycleObserver(context),
+      m_taskRunner(TaskRunnerHelper::get(TaskType::UnspecedTimer, context)),
+      m_callback(this, callback) {}
+
+MojoResult MojoWatcher::watch(mojo::Handle handle,
+                              const MojoHandleSignals& signalsDict) {
+  ::MojoHandleSignals signals = MOJO_HANDLE_SIGNAL_NONE;
+  if (signalsDict.readable())
+    signals |= MOJO_HANDLE_SIGNAL_READABLE;
+  if (signalsDict.writable())
+    signals |= MOJO_HANDLE_SIGNAL_WRITABLE;
+  if (signalsDict.peerClosed())
+    signals |= MOJO_HANDLE_SIGNAL_PEER_CLOSED;
+
+  m_handle = handle;
+
+  MojoResult rv =
+      mojo::CreateWatcher(&MojoWatcher::onHandleReady, &m_watcherHandle);
+  DCHECK_EQ(MOJO_RESULT_OK, rv);
+
+  m_context.reset(new CrossThreadPersistent<MojoWatcher>(this));
+  rv = MojoWatch(m_watcherHandle.get().value(), m_handle.value(), signals,
+                 reinterpret_cast<uintptr_t>(m_context.get()));
+  if (rv != MOJO_RESULT_OK) {
+    m_context.reset();
+    return rv;
+  }
+
+  MojoResult readyResult;
+  rv = arm(&readyResult);
+  if (rv == MOJO_RESULT_OK)
+    return rv;
+
+  // We couldn't arm the watcher because the handle is already ready to
+  // trigger a success notification. Post a notification manually.
+  DCHECK_EQ(MOJO_RESULT_FAILED_PRECONDITION, rv);
+  m_taskRunner->postTask(BLINK_FROM_HERE,
+                         WTF::bind(&MojoWatcher::runReadyCallback,
+                                   wrapPersistent(this), readyResult));
+  return MOJO_RESULT_OK;
+}
+
+MojoResult MojoWatcher::arm(MojoResult* readyResult) {
+  // Nothing to do if the watcher is inactive.
+  if (!m_handle.is_valid())
+    return MOJO_RESULT_OK;
+
+  uint32_t numReadyContexts = 1;
+  uintptr_t readyContext;
+  MojoResult localReadyResult;
+  MojoHandleSignalsState readySignals;
+  MojoResult rv =
+      MojoArmWatcher(m_watcherHandle.get().value(), &numReadyContexts,
+                     &readyContext, &localReadyResult, &readySignals);
+  if (rv == MOJO_RESULT_OK)
+    return MOJO_RESULT_OK;
+
+  DCHECK_EQ(MOJO_RESULT_FAILED_PRECONDITION, rv);
+  DCHECK_EQ(1u, numReadyContexts);
+  DCHECK_EQ(reinterpret_cast<uintptr_t>(m_context.get()), readyContext);
+  *readyResult = localReadyResult;
+  return rv;
+}
+
 void MojoWatcher::onHandleReady(uintptr_t context,
                                 MojoResult result,
                                 MojoHandleSignalsState,
-                                MojoWatchNotificationFlags) {
-  // It is safe to assume the MojoWatcher still exists because this
-  // callback will never be run after MojoWatcher destructor,
-  // which cancels the watch.
-  MojoWatcher* watcher = reinterpret_cast<MojoWatcher*>(context);
-  watcher->m_taskRunner->postTask(
+                                MojoWatcherNotificationFlags) {
+  auto* watcher =
+      reinterpret_cast<CrossThreadPersistent<MojoWatcher>*>(context);
+  (*watcher)->m_taskRunner->postTask(
       BLINK_FROM_HERE,
-      crossThreadBind(&MojoWatcher::runReadyCallback,
-                      wrapCrossThreadWeakPersistent(watcher), result));
+      crossThreadBind(&MojoWatcher::runReadyCallback, *watcher, result));
 }
 
 void MojoWatcher::runReadyCallback(MojoResult result) {
@@ -116,13 +155,40 @@ void MojoWatcher::runReadyCallback(MojoResult result) {
   if (!m_handle.is_valid())
     return;
 
-  // MOJO_RESULT_CANCELLED indicates that the handle has been closed, in which
-  // case watch has been implicitly cancelled. There is no need to explicitly
-  // cancel the watch.
-  if (result == MOJO_RESULT_CANCELLED)
+  // MOJO_RESULT_CANCELLED indicates that the watch has been cancelled, either
+  // explicitly or implicitly due to handle closure. The context object can be
+  // safely deleted at this point.
+  if (result == MOJO_RESULT_CANCELLED) {
     m_handle = mojo::Handle();
+    m_context.reset();
+
+    // If cancellation was due to an explicit |cancel()|, don't run the watch
+    // callback for this notification.
+    if (!m_watcherHandle.is_valid())
+      return;
+
+    m_watcherHandle.reset();
+    runWatchCallback(m_callback, this, MOJO_RESULT_CANCELLED);
+    return;
+  }
 
   runWatchCallback(m_callback, this, result);
+
+  // Rearm the watcher so another notification can fire.
+  //
+  // TODO(rockot): MojoWatcher should expose some better approximation of the
+  // new watcher API, including explicit add and removal of handles from the
+  // watcher, as well as explicit arming.
+  MojoResult readyResult;
+  MojoResult rv = arm(&readyResult);
+  if (rv == MOJO_RESULT_OK)
+    return;
+
+  DCHECK_EQ(MOJO_RESULT_FAILED_PRECONDITION, rv);
+
+  m_taskRunner->postTask(BLINK_FROM_HERE,
+                         WTF::bind(&MojoWatcher::runReadyCallback,
+                                   wrapPersistent(this), readyResult));
 }
 
 }  // namespace blink